1. Field of the Invention
The present invention relates to an antenna device used in various radio communication devices such as a cellular phone having a case with folding structure, turning structure, sliding structure or the like and, for example, to an antenna device and a radio communication device of which radiation patterns can be switched by an opening or closing operation of the case unit.
2. Description of the Related Art
For an antenna used in various radio communication devices such as a cellular phone, radiation efficiency is used to evaluate a property of the antenna. Since the radiation efficiency varies by a distance between the antenna and a ground conductor, a matching circuit or the like, improvement in the antenna characteristics is relatively easy by adjusting the radiation efficiency, however, for the radio communication device used in close proximity to a human body, it is known that the radiation pattern is affected by the human body.
Conventionally, for a radio communication device with folding structure, Japanese Patent Application Laid-Open Publication No. 1998-84406, for example, discloses one equipped with a conductor that is a passive element, along with an antenna. This has been proposed in order to improve significant degradation of the antenna characteristics when the case is folded. By providing a first case and a second case, an antenna disposed in the first case is positioned between the first and second cases when the first and second cases are folded, and a passive element disposed in the second case is arranged in parallel with the antenna when the first and second cases are folded. By electrically relating the antenna to the passive element when the first and second cases are folded, the passive element acts as an antenna and thus a configuration of two-element antenna is employed.
By the way, in the radio communication device such as a cellular phone, even if the configuration to operate as two-element antenna (Japanese Patent Application Laid-Open Publication No. 1998-84406) improves the antenna characteristics in a folded state, the antenna characteristics are not improved when the first and second cases are in an open state and, in the situation that the device is used in close contact with the head of a human body, radiation pattern is affected by the human body.
Japanese Patent Application Laid-Open Publication No. 1998-84406 does not disclose these problems nor a configuration and suggestion for resolving the problems exists.